Terminal 21 is another enormous shopping mall in Bangkok.
I have to admit that I am not sure of the reason to go in this one rather than another?
They are all a bit different so I would imagine that it is a personal choice which one you visit...
This one is Asok so it is easy to get to from the BTS.
Phone Number: 02 108 0888
Approximate Price: $$$$$
Address: 88 Soi Sukhumvit 19
Hours: 10am - 10pm